1. Technical Field of the Invention
The present invention generally relates to transmission of Time Division Multiplex (“TDM”) traffic over packet switched networks in Virtual Private LAN Service (“VPLS”). More particularly, and not by way of any limitation, the present invention is directed to method and apparatus for distance-sensitive scheduling of such high-priority traffic.
2. Description of Related Art
Time Division Multiplex (“TDM”) technology has been prevalent for a long time; however, the technology for transmitting TDM traffic over packet networks is relatively new. Accordingly, there are few solutions that address the problem of delay for TDM traffic when it is sent over a packet network. One solution addresses the delay that results from sending a large TDM packet over a packet network using a common switch fabric resource for TDM and packet switching. In particular, large packets or data streams are divided into smaller portions upon entering a switch. Each portion is assigned a high priority for transmission and a tracking header for tracking it through the switch. Prior to exiting the switch, the portions are reassembled into the data stream. This technique of providing “cut-through” using a store-and-forward switch mechanism reduces transmission delay and buffer over-runs that would otherwise occur in transmitting large packets or data streams. This solution strictly addresses the problem of sending only large TDM packets and does not address the specific problem of prioritizing between traffic from multiple TDM streams in a VPLS network.
Another solution involves the use of a multi-port link interface module that terminates two or more high-speed TDM links and generates internal data. Data received on one high-speed communications link is combined with the internal data used to fill outbound time slots in an outgoing high-speed link. This solution fails to address the issues of delay when sending TDM traffic over a packet network.
Currently, TDM traffic, such as voice, when sent over a packet network may suffer unacceptable delay and jitter due to multiplexing with packet data. The benefits of low cost and high bandwidth utilization of packet data networks may be offset by the poor performance of TDM traffic when sent over packet networks.
Existing traffic scheduling mechanisms that prioritize one class of traffic over another do not address the problem because all TDM traffic belongs to a single high-priority traffic class. Existing methods do not preferentially prioritize traffic within a class.